Radio receiving apparatus



A ril 24, 1928. 1,667,513

C. J. FITCH RADIO RECEIVING APPARATUS Filed May 31, 1924 2 Sheets-Sheet l QT QI "Ea-4T H l l l l l hlu d l l l l l l ln-F N C. J. FITCH RADIO RECEIVING APPARATUS 2 Sheets-Sheet 2 April 24, 1928.

Filed May 31, 1924 LE 10 INTERMZCDIATF 'E AMPLIFIER I QENTOR Patented Apr. 24, 1928.

UNITED STATES PATENT OFFICE.*

CLYDE J. FITCH, OF BROOKLYN, NEW YORK, ASSIGNOR, IBY DIRECT AND MESNE LS- SIGNMENTB, TO RADIO CORPORATION 01 AMERICA, OF NEW YORK, N. Y., A COB- PORATION OF DELAWARE.

RADIO RECEIVING APIPABATUS.

Application filed May 31, 1924. Serial 110. 717,118.

Special objects of this invention are to provide for the connection of two or more tuned circuits to the input or grid and filament terminals of a vacuum tube in such a way that said circuits will be independent of each other for tuning purposes and so that the tuning of one will not affect the tuning of the other or others and irrespective of whether the circuits be tuned tothe same or difierent frequencies.

A further purpose is to bring about a relation such that alternating currents flowing in any one of th circuits will not produce any .appreciable'current flow in the other tuned circuits even though they may be tuned to the same frequency.

One of the uses of the invention is to provide a non-radiating regenerative receiver and this is effected by using the two independently tuned circuits, one coupled to the aerial system and the other employed for regenerative purposes. Because of the independence of thetwo circuits maintained by thisinvention, even though the feed back be increased to thepoint where the tube gencrates oscillations, this current will flow only in one of the tuned circuits and will not be radiated by the aerial system.

Another important use of the invention is for heterodyning. .In such a case, one of the circuits willbe tuned to the frequency of the incoming signal and the other to the frequency of the oscillating current generated by the tube, the beat note being the difference between the two frequencies and being audible or inaudible according to the adjustment of the oscillator circuit. In receivers of the super-heterodyne type, this beat note is kept inaudible and amplified by the long wave radio frequency amplifier known as the intermediate amplifier.

In the drawings accompanying and forming part of this specification, the invention is illustrated in several of its different adaptations, but it should be understood that the structure and uses may vary 'without departure from the broad spirit and scope of the invention as claimed.

Figure l is a diagrammatic view showing the invention embodied in a simple, regenerative receiving set or in a frequency changer.

Figure 2 is a similarview 'of the'inven- 'tery is shown at B.

hereinafter defined and is varied wit igure 4 is an illustration of a modified form of the invention shown in Figure 2.

Figure 5 is a modification of the Figure 1 construction with a loop aerial. substituted in place of one of the coils.

Figure 6 is a diagram illustrating three circuits independently connected to the input of the tube.

Where possible, we have used conventional symbols and designations to represent known parts in the several views. Thus in Figure 1 the filament, grid and plate of a three electrode vacuum tube are designated F, G and P respectively, the filament battery is indicated at A and the plate bat- In the plate circuit PF is the tickler or feed back coil L and bypass condenser G. The grid circuit 2 is shown connected at P with the elec-' -trical center or nodal point of circuit 1.

This nodal connection may be the center turn of the'coil L In operation, supposing the primary coil L connected with an aerial and ground, and circuit 2 tuned to the frequency of the incoming signal, oscillations are induced in circuit 2 and because of the nodal connection through circuit 1, this current is impressed upon the grid and filament of the tube without setting up oscillations in circuit -1 even though circuit 1 be also tuned to the frequency of the incomin signal. It-

'is assumed that the coils L and are placed in a non-inductive relation with each other The reason for this is that the signal current on reaching point P divides equ'ally in coil L and charges both sides of the condenser C equally at the same polarity. On

reaching the respect to the filament and }grid. the potential of the by the usual relay action of the tube, a simi-.

lar current is repeated in the plate circuit, flowing through the coil L This tickler coil being coupled to circuit 1 and circuit 1 being tuned to the frequency of the signal, the current from coil L will be fed back into circuit, 1, resulting in amplification by regeneration.

current will not be radiated into the am tenna circuit. The circuit of Figure 1 therefore provides a very desirable form of nonradiating re 'enerative receiver.

The circuit 0 Figure 1 may also be used as afrequency changer for super-.heterodyne sets, circuit 2 being then tuned to the frequency of the incoming signal and circuit 1 being coupled to the plate circuit at L to generate an oscillating current of a different fre uency, the two being impressed on the gri and producing a beat note which is detected b the tube and then amplified by an interme iate amplifier connected to the output terrninals T. As with this arrangement the tuning of one circuit does not change the tuning of the other, a simply tuned one tube frequency changer is provided which will take the place of the two tubes heretofore required in which one serves as an oscillator and the second as a detector.

The underlying principle illustrated in Figure 1 may be carried out in various ways. Thus in place of coupling the coil L to circuit 2, it may be coupled to circuit 1 and coilL may be coupled to circuit 2, the action of the circuit and the results following being practically the same. As another variation, the tube connections F and G may be reversed. Also the plate circuit may be coupled to both circuits 1 and 2 so as to feed back into both circuits and produce greater amplification. The input circuit coil L also may be coupled to both circuits 1 and 2.

When it is desired to use the tube also as a detector, better results are obtained by using a grid condenser and grid leak which seem to operate best when connected as in Figure 2; that is, with the grid condenser C interposed in the connection to the nodal point and the grid leak it connected between the free end of the coil L and the filament connection F.

The operation then follows the action of a Wheatstone bridge in the manner indicated in Figure 3, from which it will be seen that when the values of the various units are properly chosen, the bridge will be balanced cuits will produce no current flow in the other, even though both circuits be tuned to the same frequency and also tuning one circuit will have no effect on the tuning of the other. In 'this analytical diagram, the fourth side of the bridge, that is, the rid to filament impedance, is represented %y the resistance R In practice it has been found thatthe center turn of the coil L is close enough to the theoretical center .to give satisfactory results and when the invention is used as a frequency changer in a super-heterodyne receiver the tap P even may be'placed several turns one-or the other side of the center turn without seriously affecting the operation.

-In Figure 4 another method of obtaining the center connection is shown, wherein two condensers C are arranged in series across the coil L and the center'connection- P is made between these condensers. Since these condensers will operate as grid condensers, a grid leak is shown at R in this figure.

A loop aerial such as indicated in Figure 5 may be substituted in place of the trans- .former coils in either of the tuned circuits illustrated in Figures 1 and 2.

Figure 6 illustrates in simplified form how two or more circuits may be independently connected in the grid circuit of a tube, three of the circuits being shown numbered 1, 2 and 3. .It will be apparent from this view that any number of circuits may be added, within practical limits.

What is claimed is:

1. The combination of a valve, of a pair of condensers in series, means for impress ing a signal wave on the inner sections thereof, a circuit connecting the outer section of one condenser with the grid and a circuit connecting the outer section of the loo other condenser to the filament, said latter circuit including an impedance equal to the input impedance of the tube.

2. The combination of a three electrode valve regeneratively connected, a circuit associated therewith forimpressing signals on the valve, a divided capacity having one end connected to the grid, two parallel branches one comprising the input of the valve and a portion of the capacity, the other branch comprising the other portion of the capacity and a balancing impedance equivalent to that of the valve, said branches being joined at the filament of the valveand the midpoint of the capacity and said first men-- tioned circuit having a portion connected across said junctions of the branches whereby the first mentioned circuit is defended from oscillations of the valve.

3. The combination of a three electrode m5 so that currents flowing in one of the cirhaving one end connected to the grid, an inductance in parallel with said divided ca-- pacitv said inductance being coupled to the output circuit, two parallel branches one comprising the input of the valve and a portion of the capacity, the other branch comprising the other portion of the capacity and a balancin impedance equal to that of the valve, said branches being joined at the filament of the valve and the midpoint of the capacity and said first mentioned circuit having a portion connected across the junctions of said branches.

4. The combination with a valve having back coupling between the input and output circuits of the valve for the production of oscillations, a pair of circuits connected to the input circuit of the valve, one of said circuits being tuned to the signal frequency and the other to an oscillation fre uency differing from the signal frequency y an amount corresponding to a superaudible frequency said circuit tuned to the oscillation frequency comprising inductance and capacity In parallel connected, at a junction point to the grid and back coupled to the putput circuit and said circuit tuned to the, signal having one end connected symmetrically to the inductance of the circuit tuned to the oscillation frequency and the other end' connected to the cathode of the valve,

whereby the oscillation frequency is excluded from the circuit tuned to the signals and the output circuit responsive to the superaudible beat frequency. f

5. The superheterodyne recited in claim 4 having an amplifier connected in the out- CLYDE J. FITCH. 

